The present invention relates generally to a means for monitoring the presence of acetylene (i.e. acetylene gas) in a fluid such as, for example, a dielectric fluid (e.g. a dielectric liquid or a dielectric gas).
More especially, this invention relates to a detecting device in which the concentration of acetylene dissolved in a fluid is determined by the measure of an electric current generated by electrochemical oxidation of the gaseous acetylene at a detection electrode.
The present invention may in particular, for example, be exploited as part of a means for the monitoring (e.g. detection) of acetylene in fluid insulated electrical equipment, e.g. to monitor incipient failure conditions. The dielectric fluid may be a dielectric liquid (e.g. oil) or a dielectric gas. More particularly, the present invention relates to an apparatus and method for monitoring acetylene in a dielectric fluid disposed in an interior of an electrical system wherein the dielectric fluid may be subjected to analysis.
The following will deal, by way of example only, with the detection of a gas in a fluid which is a dielectric fluid.
Electrical systems are well known in the art which use a dielectric fluid as an insulating substance; these systems include for example transformers, circuit breakers and the like.
It is known that, in the event of a disturbance or malfunction of an above mentioned type of device or system, the result may be the production of one or more gases in the insulating fluid; this may occur for example if a device is working at high temperature or high conditions of electrical stress therein. Such conditions may also produce undesired moisture and/or one or more breakdown products of the dielectric material of the insulating system (i.e. insulating fluid). If such abnormal conditions are allowed to continue uncorrected, this may lead to irreparable damage to the electrical system. A timely (e.g. more or less immediate) detection and/or diagnosis of any such abnormal operation of an electrical apparatus is thus advantageous in order to be able to avoid irreparable harm to such a system.
Accordingly, various monitoring devices and systems have been proposed for the detection of any incipient failure conditions such as for example any undesired increase of the concentration of a fault gas (e.g. a combustible gas such as for example, hydrogen gas, carbon monoxide gas, methane gas, ethane gas, ethylene gas, acetylene gas and the like or a non-combustible gas such as for example, carbon dioxide), moisture (e.g. water), a breakdown product, contaminant substance, and/or the like contained (e.g. dissolved) in the insulating fluid.
Some such detection and/or monitoring systems are, for example, described in Canadian Patent no. 1,054,223 (Bxc3xa9langer), U.S. Pat. No. 4,112,737 (Morgan), U.S. Pat. No. 4,293,399 (Bxc3xa9langer et al), U.S. Pat. No. 4,271,474 (Bxc3xa9langeret al), U.S. Pat. No. 5,070,738 (Morgan) and U.S. Pat. No. 5,271,263 (Gibeault). The entire contents of these patent references as well as any other patent or other types of references which are mentioned therein are incorporated herein by reference.
U.S. Pat. No. 5738773 for example illustrates a fuel cell arrangement for detecting oxidisable components of a gas or vapour. The fuel cell comprises first electrode means and second counter electrode means which are connected by an acidic electrolyte. The electrochemical oxidation of a fuel component in the gas results in the formation of a potential difference between the first and second electrode means; the resultant current and/or potential difference can be detected and associated with the presence and /or concentration of combustible gas detected thereby.
U.S. Pat. No. 4,293,399, for example, describes how the concentration of gaseous hydrogen dissolved in a fluid may be determined by a measure of an electric current generated by electrochemical oxidation of the gaseous hydrogen at an electrode of the detector; i.e. by a measure of a current generated in response to the presence of hydrogen (in a gas). The prior art detecting and measuring means described in this U.S. patent comprises a polymeric membrane permeable to hydrogen gas for contact with a fluid containing dissolved hydrogen gas; an electrolyte capable of facilitating oxidation of the hydrogen gas diffused through the polymeric membrane at a first electrode and reduction of an oxygen-containing gas such as air at a second electrode; and a measuring device connected to the fuel cell for measuring the intensity of the electrical current generated by the electrochemical reaction of oxidation of the hydrogen gas, this intensity being proportional to the concentration of hydrogen in the fluid. See also Canadian Patent no. 1,054,223 (Bxc3xa9langer) mentioned above.
It is advantageous for such monitoring (e.g. detection) devices, as described above, to be able to provide an accurate as possible detection and/or diagnosis of the incorrect operation of systems such as, for example, transformers, circuit breakers, shunt reactors or any electro-apparatuses using a dielectric fluid as an insulating substance such as a dielectric liquid (e.g. a dielectric oil) or a dielectric gas (e.g. SF6 gas).
A number of the above mentioned prior art monitoring devices or systems have the drawback that the sample gas received by the detector may have a relatively low concentration of a target gas which it is desired to detect or monitor; e.g. a low concentration of acetylene gas relative to hydrogen gas. In such case, the low concentration of a target gas relative to the other gases present in a sample gas may be such that one or more of the other gases may interfere with the measurement of a predetermined target gas(es). In other words, the precision of the results of the detecting or monitoring device may thus be less than is desired; i.e. due to that fact that one or more extraneous gases may interfere with the reading of the target gas (e.g. acetylene).
The presence, concentration and evolution of even very low concentrations of acetylene dissolved in a dielectric fluid, such as for example a dielectric oil, is a particularly useful indicator of the processes occurring (e.g. default gas production) in the insulated electrical equipment. As mentioned, in addition to acetylene, the dielectric fluid may contain other dissolved gases, such as hydrogen, carbon monoxide, ethylene, ethane, methane, etc.. A reliable analysis of acetylene thus requires a detector having an enhanced selectivity for acetylene at very low concentrations in the presence of other such dissolved gases.
Accordingly, it would be advantageous to have a detector for the specific detection and monitoring of acetylene dissolved in a dielectric fluid such as for example a dielectric oil
It would, in particular, be advantageous to be able to perform the analysis (e.g. detection) of a target gas such as acetylene which forms part of a sample gas mixture.
It is to be understood herein that the expression xe2x80x9csensor componentxe2x80x9d as well as the words xe2x80x9csensorxe2x80x9d, xe2x80x9csensingxe2x80x9d and the like include, but are not limited to, activities which involve checking for a substance, detecting a substance, determining the presence of a substance, etc..
It is also to be understood herein that the expression xe2x80x9canalysing means for monitoringxe2x80x9d as well as the words xe2x80x9cmonitorxe2x80x9d, xe2x80x9cmonitoringxe2x80x9d and the like include, but are not limited to, one or more activities which involve checking for a substance, detecting a substance, keeping track of a substance, determining the presence of a substance, the continuous measurement of a substance, the intermittent measurement of a substance, etc..
The present invention in accordance with one aspect provides an electrochemical cell (e.g. fuel cell), for generating a current in response to the presence of acetylene in a fluid (e.g. in a gas such as for example a gas sample), said fuel cell comprising first and second gas porous electrode means, and acidic electrolyte means interconnecting said first and second electrode means for facilitating the electrochemical oxidation of the acetylene at said first electrode means and the electrochemical reduction of oxygen in an oxygen-containing gas at said second electrode means so as to generate said current, said first electrode means being a gas porous gold electrode means. It is to be understood herein that the expression xe2x80x9cacidic electrolytexe2x80x9d, xe2x80x9cacidic electrolyte meansxe2x80x9d and the like refers to an acidic proton conductor electrolyte; e.g. a reference to an acidic solid (e.g. a substrate such as for example a suitable polymeric material) electrolyte is a reference to an acidic proton conductor solid (e.g. polymer) electrolyte. The electrochemical cell (e.g. fuel cell) in accordance with the present invention may be incorporated into an apparatus, sensor, device, system, etc., for monitoring acetylene in a dielectric fluid, e.g. by generating a current in response to the presence of acetylene in a gas sample.
In accordance with the present invention, the electrode means may for example, consist of a single first gas porous electrode component or element and a single second gas porous electrode component or element.
In accordance with the present invention the first electrode means may for example be a gold electrode means which may comprise a gas porous gold layer (e.g. thin metallic layer) interfacing with a solid electrolyte substrate, i.e. the gold layer and the electrolyte substrate may define a gas porous gold/electrolyte interface zone wherein gold may be intertwined with the matrix of the substrate at least adjacent the outer surface of the substrate associated with the gold layer. Suitable solid electrolyte substrates are discussed below. The gas porous metallic gold layer (e.g. thin layer) is configured such that acetylene may pass therethrough to the gold/electrolyte interface zone.
In accordance with an additional aspect the present invention provides an electrochemical cell (e.g. fuel cell), for generating a current in response to the presence of acetylene in a fluid (e.g. in a gas such as for example a gas sample), said fuel cell comprising electrode means, said electrode means comprising or consisting of first and second gas porous electrode components, and electrolyte means interconnecting said first and second electrode means for facilitating the electrochemical oxidation of the acetylene at said first electrode means and the electrochemical reduction of oxygen in an oxygen-containing gas at said second electrode means so as to generate said current, wherein said electrolyte means is an acidic electrolyte means, wherein said first electrode component may, for example, comprise a gas porous gold film or layer interfacing with an acidic solid electrolyte substrate and wherein said second electrode component may, for example, comprise a noble metal film or layer also interfacing with an acidic solid electrolyte. The first electrode component may, for example, comprise a gold film or layer which is deposited on an acidic solid electrolyte substrate as discussed herein below. The second electrode component may, for example, comprise noble metal (e.g. Au, Pt, and the like including mixtures (i.e. alloys) thereof) film or layer which is deposited on an acidic solid electrolyte substrate as discussed herein below. The electrolyte/electrode means combination may take on any suitable or desired configuration; for example the combination may comprise a gel electrolyte interposed between the first and second electrode components, the gel electrolyte being in contact with the respective acidic solid electrolyte substrates; alternatively the combination may, for example, comprise the first and second electrode components, but wherein the gold and noble metal films interface opposite sides a common solid electrolyte substrate; and the like.
The present invention further provides a sensor device for generating a current in response to the presence of acetylene in a fluid (e.g. in a gas such as for example a gas sample), said sensor device comprising an electrochemical cell (e.g. fuel cell), said cell comprising electrode support means, first and second gas porous electrode means, and acidic electrolyte means interconnecting said electrodes for facilitating the electrochemical oxidation of the acetylene at said first electrode, and the electrochemical reduction of oxygen in an oxygen-containing gas at said second electrode so as to generate said current, said first electrode means being a gas porous gold electrode means. In accordance with the present invention a sensor device as described herein may comprise a first channel means for bringing the fluid (e.g. gas) containing acetylene to said first electrode and second channel means for bringing said oxygen containing gas to said second electrode. The acetylene may be in a gas sample extracted from a dielectric fluid (e.g. acetylene dissolved in a liquid substance may be extracted in any suitable (known) manner for this purpose).
The present invention in another aspect provides in a system or an apparatus for monitoring gas in a dielectric fluid, said fluid being in an interior of an electrical system, the system or apparatus comprising:
a)gas extraction means for extracting a gas mixture from said fluid, said gas mixture comprising two or more gas components, one of said gas components being acetylene; and
b) analysing means for monitoring the presence of acetylene in said gas mixture,
the improvement wherein said analysing means includes a sensor device for generating a current in response to the presence of acetylene in said gas mixture, said sensor device comprising an electrochemical cell (e.g. fuel cell), said fuel cell comprising electrode support means, first and second gas porous electrode means, and acidic electrolyte means interconnecting said electrodes for facilitating the electrochemical oxidation of the acetylene at said first electrode and the electrochemical reduction of oxygen in an oxygen-containing gas at said second electrode so as to generate said current, said first electrode means being a gas porous gold electrode means. The gas extraction means may for example comprise a gas extraction membrane as described herein, the membrane being permeable to acetylene and one or more other gases (preferably the membrane has a high permeability to acetylene and a low permeability to other gases) .
In accordance with the present invention, the current generated by the fuel cell may, for example, be measured in any suitable known manner e.g. by measuring the voltage drop across a suitable electrical load (e.g. across a suitable load resistance).
The reaction of the sensor fuel cell means of the present invention theoretically occurs as follows:
a) At the first electrode means (i.e. gold electrode means), with acidic electrolyte media, the electrooxidation of acetylene take place, resulting in negative charging of the first electrode means. The reaction is favoured by the electrocatalytic properties of gold as follows:
C2H2+4H2O=2CO2+10H++12exe2x88x92
b) Simultaneously, to oxygen present at the second counter electrode means (e.g. platinum electrode means) is electrochemically reduced producing the positive charging of the second electrode means as follows:
3O2+12H++12exe2x88x92=6H2O
c) The global reaction in the fuel cell produces two molecules of water for each reacting acetylene molecule as follows:
C2H2+3O2+2H+=2CO2+2H2O
The electrolyte used is to be of such a composition so as to enable the occurrence of the reaction of electrochemical oxidation of the acetylene at the first electrode and that of reduction of oxygen at the second electrode; in general the electrolyte is acidic. For that purpose, any type of acidic electrolyte respecting the electrochemical operation principle of the detector in accordance with the present invention may be used. Thus the oxido-reduction reaction can be initiated by means of an electrolyte constituted by an acid, such as phosphoric acid, sulfuric acid or perchloric acid. The electrolyte may be a gel electrolyte, i.e. an electrolyte gelled by a conventional gelling agent(s) such as Cabxe2x80x94Oxe2x80x94Sil (trademark) fumed silica from Cabot Corp. Boston, Mass. U.S.A . . . It may, for example, be a gel electrolyte comprising sulfuric acid. On the other hand, the electrolyte may be a solid acidic proton conductor electrolyte which may for example be a solid polymeric electrolyte; the electrolyte may in particular be a solid ion conducting substrate such as for example a Perfluorosulfonic Acid Polymers. One type of such solid electrolytes are the Nafion (copyright) Perfluorosulfonic Acid Polymers available from DuPont Nafion products, Fayetteville, N.C. U.S.A; hereinafter these types of membranes or substrates will unless otherwise indicated be referred to simply as Nafion. Other proton conducting membranes or substrates may for example be obtained from Dow chemical U.S.A.; Ormocers may also possibly be used (i.e. organically modified ceramics); examples of other suitable membranes or substrates may be gleaned from xe2x80x9cPolymeric Electrolytesxe2x80x9d, by Fiona M. Gray, RSC Materials Monographs, Ed. The Royal Society of Chemistry, Cambridge, U.K. 1997.
In accordance with the present invention the first electrode means may comprise gold, i.e. be a gold electrode means. In accordance with the present invention the first electrode (e.g. gold electrode) may have a electro-catalytic activity for favouring the oxidation of acetylene as against the oxidation of gases like hydrogen, carbon monoxide, ethylene, methane, ethane and the like. The specificity of a gold electrode means for the electrochemical oxidation of acetylene may be enhanced by using modified electrode structures. In accordance with the present invention a first electrode means may for example comprise or consist of a gas porous gold film or layer (e.g. thin layer) interfacing an above mentioned solid ion conducting substrate or membrane, i.e. such that the electrode has a gold/substrate interface zone wherein gold is dispersed within the matrix of the substrate (e.g. at least adjacent the surface boundary of the substrate. The solid ion conducting membrane may be for example a Perfluorosulfonic Acid Membrane, e.g the above mentioned Nafion (copyright) Membrane(s) available from Dupont.
In accordance with the present invention, the second or other electrode means may be any other electrode means having oxygen electro-catalytic activity for the reduction of oxygen. The second electrode means may be a noble metal electrode; for example, the second electrode means may be a platinum electrode or a gold electrode means. The second electrode means, for example, may comprise at least one noble metal/carbon combination and a polymeric hydrophobic binder. The second electrode means may in particular, for example, be a gas porous (e.g. conventional gas diffusion) electrode and may comprise platinum and carbon (a suitable platinum gas diffusion electrode, for example, may be obtained from E-Tek Inc. in Natick, Mass. U.S.A.). In accordance with the present invention a second electrode means may for example alternatively comprise or consist of a gas porous gold or platinum film or layer (e.g. thin) interfacing (as described herein) a herein mentioned solid ion conducting membrane (e.g. a proton conducting substrate).
As mentioned above a first electrode means may for example comprise or consist of a gas porous gold film or layer interfacing solid ion conducting substrate such as for example a Perfluorosulfonic Acid Membrane obtainable from Dupont available under the trademark Nafion(copyright). The in situ gold electrode formation on a Nafion membrane may be carried out by following in analogous fashion the procedures described for the deposition of Platinum on Nafion in the literature such as for example in: H.Takenaka, E.Torikcai, Kokai Tokyo Koho (Japan Patent) 55, 38934 (1980); H.Takenaka et al., International Journal Hydrogen Energy 5, 397-403 (1983); J-T.Kita and H, Nakajima, Electrochimica Acta, Vol. 31, 193-200, 1986; and R. L.Cook, et al., J. Electrochern, Soc, 137,187-189,(1990).
In accordance with the present invention a sensor means for monitoring the acetylene content of a dielectric fluid may for example have three separate modules, namely: a base, a hollow housing, and a mounting means for the first and second electrodes. The base and the hollow housing may configured so as to be releasably attached (i.e. in known fashion) to the receptacle containing the fluid whose acetylene content is to be monitored. The base contains a channel therethrough and is connected to a similar channel in the hollow housing. Placed between the base and the hollow housing is a requisite gas extraction membrane (e.g. polymeric membrane) which is able to perform extraction of acetylene dissolved in dielectric fluid (e.g. oil); it preferably should have a high permeability to acetylene and a low permeability to the other gases which may be in the dielectric fluid. The electrodes and electrolyte may be provided in a mounting unit which is removably insertable in the hollow housing so that it can be independently removed for maintenance without disturbing the gas extraction membrane. This mounting unit may include a bucket-shaped container the top of which is closable by means of a cap. The first electrode means may mounted between first and second holding elements and the second electrode means may be mounted between second and third holding elements, such that the two electrodes are spaced apart by an electrolyte. The individual holding elements inserted into the housing element may all have a central aperture therethrough such that the first electrode means is in fluid communication with the polymeric membrane and the other second electrode is in fluid communication with an oxygen-containing gas (e.g. air). Thus, the passage of acetylene through the polymeric membrane will cause oxidation of the acetylene at the first electrode and reduction of oxygen at the second electrode generating a signal therebetween which is indicative of the acetylene concentration in said fluid.
The present invention further provides a compact acetylene sensor device which may be used for detecting and measuring (e.g. monitoring) the concentration of acetylene dissolved in a fluid contained in a receptacle having a wall provided with a valved opening i.e. an opening blocked by a valve. The compact acetylene sensor device may be used to monitor acetylene in fluid sampled from the valve. The compact acetylene sensor device may be mounted to the valve using structure(s) the same as or analogous or similar to the structure shown in U.S. Pat. No. 5,773,709 for so mounting the therein described sensor device 90. The compact acetylene sensor device of the present invention may provide an electrical signal indicative of the presence and/or concentration of acetylene in the fluid sample.
The compact acetylene sensor device of the present invention may comprise:
a probe base body comprising a holding element having a socket opening, and a channel member having a central channel therein and an exterior threaded portion;
a gas extraction membrane means (e.g polymeric membrane) for contact with said fluid and permeable to acetylene gas, said membrane being disposed between the channel member and the holding element such that the membrane means separates the central channel and the socket opening;
means for defining an intermediate fuel cell cup insertable in said socket opening and having a bottom, said intermediate fuel cell cup including means defining an aperture in said bottom;
means for sealingly mounting said intermediate fuel cell cup in said socket opening such that said gas extraction membrane means is sealingly disposed (i.e. in fluid tight fashion) between said intermediate fuel cell cup and said base body, said gas extraction membrane means preventing the passage of the fluid (i.e. liquid) therethrough and permitting the passage of acetylene gas from said channel to and through said aperture in said intermediate fuel cell cup;
means for defining an inner fuel cell cup insertable in said intermediate fuel cell cup and having a bottom, said inner fuel cell cup having means an aperture in the bottom thereof, the apertures in the bottom of the intermediate and inner fuel cell cups being in fluid communication,
a fuel cell element insertable in said inner fuel cell cup, said fuel cell element comprising housing means, first and second gas porous electrode means, and electrolyte means for facilitating the electrochemical oxidation of the acetylene at said first electrode means, and the electrochemical reduction of oxygen in an oxygen-containing gas at said second electrode means so as to generate said current, said housing means having a wall component comprising said first and second electrode means, said electrolyte means being disposed in said housing means so as to separate said electrode means and said first electrode means being a gas porous gold electrode;
a holding element having a member insertable in said inner fuel cell cup, said holding element including means defining an opening therein;
a removeable intermediate cover plate for closing off said intermediate fuel cell cup sealing means disposed such when said intermediate cover plate is mounted to the intermediate fuel cell cap said fuel cell element is sealingly sandwiched between said inner fuel cell cup and said holding element, said first electrode being sealingly disposed opposite said aperture in said inner fuel cell cup, said second electrode being sealingly disposed opposite said opening in said holding element, said intermediate cover plate including means defining an opening therein; the openings in said holding element and said intermediate cover plate being in fluid communication,
a probe cap element covering the socket opening of the holding element so as to define, between the probe cap and the intermediate cover plate, a gap chamber, said probe cap element being held to said holding element by a second holding element, means sealingly mounting said probe cap to said socket opening, said probe cap element having an opening there through in fluid communication with said gap chamber, air permeable cover means covering said opening.
The first and second electrode means of the above compact acetylene sensor device may be electrically connected by any (known) suitable means such as by noble metal strips or foil elements (e.g. of Pt or Au) to other connector elements such as wires for final connection to a suitable fixed load resistance (e.g. a resistance of from 500 to 2200 ohms). A (known) measuring device may then be attached to the load resistance so as to be able to permit one to measure the voltage developed across the load resistance.
For the above described compact acetylene sensor device, an ion conductive electrolyte may be substantially contained within the electrolyte chamber, which is defined at its sides by the first and second electrode means. The electrolyte chamber for example may be packed with a suitable electrolyte gel comprising an acid electrolyte such as phosphoric acid or sulphuric acid. The electrolyte may be gelled by conventional gelling agents such as Silica-Cabosil. Alternatively the electrolyte may be a solid polymer electrolyte, for example a cationic resin polymer such as Nafion.
The function of the gas extraction membrane, if present, is to allow the acetylene gas to diffuse inside the detecting unit from, for example, a dielectric liquid. The gas extraction membrane should preferably, be able to perform the extraction of acetylene dissolved in dielectric fluid (e.g. oil) at a suitable rate; it preferably should have a high permeability to acetylene and a low permeability to the other gases such as hydrogen, ethylene, carbon monoxide and other hydrocarbons which may be in the dielectric fluid; it should be impermeable to the dielectric fluid; etc ... The gas extraction membrane may, for example, be of polymeric material such as of polyethylene, polytetrafluoroethylene (or Teflon(trademark)), polypropylene, fluorosilicone or the like; the permeability of these materials may be made such as to permit diffusion of the acetylene gas therethrough. Teflon membranes may be chosen for their low permeability to water vapor and reasonable permeability to acetylene. On the other hand Polypropylene and fluorosilicone membranes may be chosen for their high permeability to acetylene. A gas extraction membrane of Teflon 1 mil thickness has been found to provide good sensitivity, good selectivity and a good detector lifetime. This membrane is a compromise between a high sensitivity to acetylene (polypropylene and flurosilicone) and low permeability to water vapour.